Peewee ORM入门与功能详解

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Peewee教程是一份针对Python开发者的指南，介绍如何使用这款轻量级且功能丰富的对象关系映射（Object-Relational Mapping, ORM）框架。它旨在提供简单易学的体验，适合初学者快速上手。Peewee的特点包括： 1. **小巧而强大**：Peewee的设计理念是简洁但表达能力强，这使得它在处理数据库操作时避免了复杂的概念，便于理解与使用。 2. **Python兼容性**：Peewee基于Python编写，支持Python 2.6及以上版本和3.2及以上的更新，确保了广泛的应用环境。 3. **数据库支持**：内置了对SQLite、MySQL和PostgreSQL等主流数据库的支持，开发者可以根据项目需求选择合适的数据库。 4. **扩展库丰富**：Playhouse是Peewee的扩展库集合，提供了许多实用的功能，如Postgres HStore、JSON支持、数组操作、SQLite全文搜索、数据库迁移工具等，极大地增强了Peewee的功能性和灵活性。 5. **文档结构**：教程按照以下章节展开： - **安装与测试**：引导读者安装并验证Peewee的运行环境。 - **快速入门**：介绍基本的使用方法和创建数据库模型的步骤。 - **示例应用**：通过实例演示Peewee在实际项目中的应用。 - **额外资源**：推荐学习资料，帮助新手深入学习。 - **数据库管理**：讲解如何管理和维护数据库。 - **模型与字段**：详细解释模型的构建和字段的定义。 - **查询操作**：涵盖了查询构造、高级查询语法等内容。 - **查询操作符**：介绍如何使用各种查询条件和操作符。 - **外键**：讨论如何处理表与表之间的关联。 - **性能优化**：分享提高性能的技巧和最佳实践。 - **事务处理**：确保数据的一致性和完整性。 - **API参考**：提供完整的接口文档供深入查阅。 - **Playhouse扩展库**：详细列出可用的附加功能模块。 6. **入门文档推荐**：对于新用户，特别推荐阅读快速入门指南，以便快速了解基础概念和用法。通过这份教程，用户可以逐步掌握Peewee的基本原理和高级功能，从而在Python开发中高效地进行数据库操作。无论是初学者还是有一定经验的开发者，都能从中找到所需的信息来提升自己的技能。

peewee Documentation, Release 2.4.0

Because SQLite likes to have a separate connection per-thread, we will tell ﬂask that during the request/response cycle

we need to create a connection to the database. Flask provides some handy decorators to make this a snap:

@app.before_request

def before_request():

g.db = database

g.db.connect()

@app.after_request

def after_request(response):

g.db.close()

return response

Note: We’re storing the db on the magical variable g - that’s a ﬂask-ism and can be ignored as an implementation

detail. The important takeaway is that we connect to our db every request and close that connection when we return a

response.

Making queries

In the User model there are a few instance methods that encapsulate some user-speciﬁc functionality:

• following(): who is this user following?

• followers(): who is following this user?

These methods are similar in their implementation but with an important difference in the SQL JOIN and WHERE

clauses:

def following(self):

# query other users through the "relationship" table

return (User

.select()

.join(Relationship, on=Relationship.to_user)

.where(Relationship.from_user == self))

def followers(self):

return (User

.select()

.join(Relationship, on=Relationship.from_user)

.where(Relationship.to_user == self))

Creating new objects

When a new user wants to join the site we need to make sure the username is available, and if so, create a new User

record. Looking at the join() view, we can that our application attempts to create the User using Model.create().

We deﬁned the User.username ﬁeld with a unique constraint, so if the username is taken the database will raise an

IntegrityError.

try:

with database.transaction():

# Attempt to create the user. If the username is taken, due to the

# unique constraint, the database will raise an IntegrityError.

user = User.create(

username=request.form[’username’],

password=md5(request.form[’password’]).hexdigest(),

email=request.form[’email’],

12 Chapter 1. Contents:

peewee Documentation, Release 2.4.0

kwargs[var_name] = qr.paginate(kwargs[’page’])

return render_template(template_name,

kwargs)

• Simple authentication system with a login_required decorator. The ﬁrst function simply adds user data

into the current session when a user successfully logs in. The decorator login_required can be used to

wrap view functions, checking for whether the session is authenticated and if not redirecting to the login page.

def auth_user(user):

session[’logged_in’] = True

session[’user’] = user

session[’username’] = user.username

flash(’You are logged in as %s’ % (user.username))

def login_required(f):

@wraps(f)

def inner(

args,

kwargs):

if not session.get(’logged_in’):

return redirect(url_for(’login’))

return f(

args,

kwargs)

return inner

• Return a 404 response instead of throwing exceptions when an object is not found in the database.

def get_object_or_404(model,

expressions):

try:

return model.get(

expressions)

except model.DoesNotExist:

abort(404)

Note: Like these snippets and interested in more? Check out ﬂask-peewee - a ﬂask plugin that provides a django-like

Admin interface, RESTful API, Authentication and more for your peewee models.

1.4 Additional Resources

I’ve written a number of blog posts about building applications and web-services with peewee (and usually Flask). If

you’d like to see some real-life applications that use peewee, the following resources may be useful:

• Building a note-taking app with Flask and Peewee as well as Part 2 and Part 3.

• Analytics web service built with Flask and Peewee.

• Personalized news digest (with a boolean query parser!).

• Using peewee to explore CSV ﬁles.

• Structuring Flask apps with Peewee.

• Creating a lastpass clone with Flask and Peewee.

• Building a web-based encrypted ﬁle manager with Flask, peewee and S3.

• Creating a bookmarking web-service that takes screenshots of your bookmarks.

• Building a pastebin, wiki and a bookmarking service using Flask and Peewee.

14 Chapter 1. Contents:

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